1. Field of the Invention
This invention relates to a process for the preparation of homopolymers and copolymers of a vinyl halide such as vinyl chloride characterized by reduced reactor scale formation. The reactor scale formed in a commercial process of bulk polymerization occurs to such an extent that it is normally required that the reactor and stirring blades be cleaned subsequent to the preparation of each batch of vinyl halide polymer. The production of reactor scale is normally much greater where high temperatures of polymerization are used to produce low molecular weight bulk polymerized polymers. The tenacity of adhesion of the scale to the reactor walls and stirring mechanism varies, but generally where the polymer scale has fused to the wall or stirring mechanism as the result of the use of high polymerization temperatures it is extremely difficult to remove such scale by mechanical means.
2. Description of the Prior Art
U.S. Pat. No. 3,725,367 to Kemp relates to the preparation of vinyl based polymers and copolymers in a single stage bulk process of polymerization in which a seeding latex of polyvinyl chloride is present during the polymerization process. Within the particles of the seeding latex there is contained a quantity of catalyst or initiator which permits initiation of the bulk polymerization process without separate addition of initiator.
It is noted that a particularly small amount of encrustation (scale) forms on the walls of the reactor during the polymerization process.
U.S. Pat. No. 3,642,745 relates to the polymerization of vinyl chloride in an aqueous medium in the absence of a dispersing agent and in the presence of a dispersion of a granular inert solid such as silica. Crusting on the polymerization reactor wall is avoided by the process.
U.S. Pat. No. 3,488,328 relates to the suspension polymerization of vinyl chloride in the presence of a suspending agent, a non-ionic surface active agent, and an organic solvent inert to the polymerization reaction so as to prevent adhesion of polymer scale to the inner wall of the polymerization vessel.
In view of these prior art references, it is surprising that a process for the bulk polymerization of a vinyl halide in contact with a small amount of water and an inert inorganic fine particle size additive such as silica would result in a reduction in the amount of reactor scale formed during the process.